Mrtinhnv wrote:
Dear Bunuel!
I can find the slope of the first line is m and the slope of the second line is 1
But I don’t know How can we find value of a if we know the slope of two lines. You can more detail.
Thanks so much!
Slope of a line is a measure of its inclination with respect to the horizontal.
The more the inclination the more will be the slope, lesser the inclination less will be the slope.
In general, slope of a line is defined as m = tan θ , where θ is the angle between the line and the horizontal axis.
(Even though trigonometry is not involved in GMAT, if you understand the concept of slope it will help you in solving
problems such as these. In fact the formula for slope m = (y
2-y
1)/(x
2-x
1) is actually derived from m = tan θ)
So, if you know slope of a line, you know the angle with which its is inclined. [tan^-1 (m)]
Since the given problem is a data sufficiency problem you dont have to solve for anything. You just need to say whether the info given is sufficient to
answer the question.
See attached figure
From the question stem you know the slope of one line which means the angle at which this line is inclined (θ
1)
From the statement 1 you know the slope of other line which means the angle at which this line is inclined (θ
2)
The difference between these two angles will give you the angle at which they are intersected.